Such a front face is particularly useful for protecting burners used for the partial combustion of carbonaceous fuels, such as finely divided solid fuel carried by a gas, e.g., pulverized coal carried by a carrier gas such as nitrogen gas or carbon dioxide, using an oxygen-containing gas, e.g., for producing pressurized synthesis gas, fuel gas or reducing gas.
Partial combustion, also known as gasification, of a solid carbonaceous fuel is obtained by the reaction of the fuel with oxygen. The fuel contains as combustible components, mainly carbon and hydrogen. The gas-carried finely divided carbonaceous fuel and the oxygen-containing gas are passed via the separate channels in the burner into a reactor at relatively high velocity. In the reactor a flame is maintained in which the fuel reacts with the oxygen in the oxygen-containing gas at temperatures above 1300° C. to form mainly carbon monoxide and hydrogen.
The term “oxygen-containing gas” as used herein is intended to refer to gas containing free oxygen, O2, and to include air, oxygen-enriched air, i.e., more than 21 mole % oxygen, and also substantially pure oxygen, i.e., more than about 95 mole % oxygen, with the remainder comprising gases normally found in air such as nitrogen, and/or rare gases.
The term “solid carbonaceous fuel” as used herein is intended to include various gas carried combustible materials and mixtures thereof from the group of coal, coke from coal, coal liquefaction residues, petroleum coke, soot, biomass, and particulate solids derived from oil shale, tar sands and pitch. The coal may be of any type, including lignite, sub-bituminous, bituminous and anthracite. The solid carbonaceous fuels are preferably ground to a particle size so that at least about 90% by weight of the material is less than 90 microns and moisture content is less than about five percent weight.
U.S. Pat. No. 4,887,962 and U.S. Pat. No. 4,865,542 disclose a burner for such a partial combustion process. The burner comprises a central channel with an outlet for supplying the fuel to the combustions zone, and a coaxial annular channel with an outlet surrounding the central channel's outlet to supply an oxygen containing gas intersecting and mixing with the flow of solid fuel from the outlet of the central channel. The burner further comprises a front face disposed at the discharge end of the burner. The front face has a central aperture through which the fuel and the oxygen containing gas flow to the combustion zone. The front face is a double walled member comprising a central aperture corresponding to the discharge end of the burner, a front side wall and a backside wall spaced by a spiral baffle defining a spiral flow path with a first end operatively connected to a coolant supply conduit and a second end having an outlet operatively connected to a coolant discharge conduit.
At the discharge end, the combustion temperatures can be as high as 1300° C. or higher. This causes thermal stresses and deterioration of the burner during prolonged operation, particularly by fatigue stresses, which may ultimately result in leaks of coolant. Moreover, during operation burner heads also undergo high mechanical pressure loads.